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Universal Track Tester

Universal Track Tester for the Layout

This low cost track tester is especially useful if you ever are involved in both analogue and digital fault finding in model railroad power systems. It will assist you in determining different sources of voltage and if a power part of the pulse Train is missing.

The very simple and straight users instruction is to press the tester across the track and read out the indication of the two LED’s. This project should be looked upon as the primary testing followed by more sophisticated instruments should you want to explore more detailed information about what is going on across the track.

This easy way of walk around testing is especially effective if you are confronted with larger layouts with lots of tracks, and want to fence off any suspected power failure.

It s up to you to make the choice of boxing for this project, and any pair of test cables with pointers will do the job electrically.

Signal interpretation
As mentioned initially this measurement is indicative. You won’t be able to readout exact voltage level. And you won’t be able to exactly identify the code of a digital system.

The easy reference is the analog power. The digital indicator is off regardless of current direction and voltage level. On the contrary the analog indicator is glowing more intensive with increasing voltage and depending on polarity across the track it will be red or green. Keep the tester down on the track and turn the speed knob into different positions to verify this.

Next step is AC and the obvious target is Märklin. If you decided to build the project into the Trix casing you will have a handy tester also for the different Märklin tracks including the new C-system. The mid rail or its visible feeder points are easy to connect if the tester is bent downwards a little and to the center. The digital indicator is constantly lit, however not bright, regardless of speed. The analogue strictly follows the voltage level.

Different digital systems
This is the time to explain the red-green indication in several icons of the guide. Mainly it indicates rapid changes in voltage polarity across the LED. A digital pulse train is a typical such an example. Various brands of LED’s behave differently. Some get an orange light as result of these rapid changes, while others tend to show somewhat more rose (extreme cases towards pink) color. And yet other brands like the ones in the prototype don’t mix the green and red to much if you look straight into the top of the LED. My own experiments show that you learn fast to make the correct interpretation after a few initial test rounds. Now let’s target the Märklin digital system with the first generation of Motorola protocol. The digital indicator is constantly lit regardless of speed, but the analog show changes all along the speed curve due to changes in the DC part of the pulse train. There is also a significant difference if the power system just had a reset and no activated addresses in comparison to having already made command to at least one loco.

Then addressing the second generation of the Märklin Motorola protocol you easily can see the difference by focusing the digital indicator. It clearly swings from red to green when changing the code by turning the speed knob.

Finally a few words about the NMRA DCC digital systems. Mainly there are two different modes you may identify. The first is the pure digital mode and the second is the mix with an analogue address – often 00 is used. In this latter case the change of speed direction is easy to identify by the change of color between red and green.

C1=22 nF
R1-R2=1 kohm

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